Gamma/Gain Nodes
declare shader "mip_gamma_gain" (
color "input",
scalar "gamma" default 1.0,
scalar "gain" default 1.0,
boolean "reverse" default off,
)
apply texture, environment, lens
version 1
end declare
This is a simple shader that applies a gamma and a gain (multiplication) if a color. Many similar shaders exists in various OEM integrations of mental ray, so this shader is primarily of interest for standalone mental ray and for cross platform phenomena development.
If reverse is off, the shader takes the input, multiplies it with the gain and then applies a gamma correction of gamma to the color.
If reverse is on, the shader takes the input, applies a reverse gamma correction of gamma to the color, and then divides it with the gain; i.e. the exact inverse of the operation for when reverse is off.
The shader can also be used as a simple gamma lens shader, in which case the input is not used, the eye ray color is used instead.
This shader allows re-rendering a subset of the objects in a scene,
defined by material, geometric objects, or instance labels. It is
the ideal "quick fix" solution when almost everything in a scene
is perfect, and just this one little object or one material needs
a small tweak1.
It is applied as a lens shader and works by first testing which
object an eye-ray hits, and {only if the object is part of the
desired subset is it actually shaded at all}.
Pixels of the background and other objects by default return
transparent black (0 0 0 0), making the final render image ideal
for compositing directly on top of the original render.
So, for example, if a certain material in a scene did not turn out
satisfactory, one can simply:
An example of using mip_render_subset on one material
Naturally, only pixels which see the material "directly" are
re-rendered, and not e.g. reflections in other objects
that show the material.
The shader relies on the calling order used in raytracing and does not work
correctly (and yields no benefit in render time) when using the rasterizer,
because the rasterizer calls lens shaders after already shading the
surface(s).
enabled turns the shader on or off. When off, it does nothing,
and does not affect the rendering in any way.
objects, instance_label and material are the
constraints one can apply to find the subset of objects to shade.
If more than one constraint is present, all must be fulfilled, i.e.
if both a material and three objects are chosen, only the object that
actually have that material will be shaded.
If one do not want to shade the subset, but only find where it is on
screen, one can turn on mask_only. Instead of shading the
objects in the subset, the mask_color is returned, and no
shading whatsoever is performed, which is very fast.
Rays not hitting any objects return the background color,
and rays hitting any object not in the subset return the
other_objects color.
Finally, the full_screen_fg decides if the FG preprocess
should apply to all objects, or only those in the subset. Since FG
blends neighboring FG samples, it is probable that a given object
may use information in FG points coming from nearby objects
not in the subset. This is especially true if the objects are
coplanar. Therefore it is advised to let the FG pre-pass "see" the
entire scene.
Naturally, turning off this option and creating FG points only for
the subset of objects is faster, but there is a certain risk
of boundary artifacts, especially in animations. If the scene uses
a saved FG map, this option can be left off.
Render Subset of Scene
declare shader "mip_render_subset" (
boolean "enabled" default on,
array geometry "objects",
array integer "instance_label",
material "material",
boolean "mask_only" default off,
color "mask_color" default 1 1 1 1,
color "background" default 0 0 0 0,
color "other_objects" default 0 0 0 0,
boolean "full_screen_fg" default on
)
apply lens
version 5
end declare